The present invention relates to improvements in apparatus for mixing granular and/or pulverulent solid constituents with liquids, especially to improvements in apparatus for mixing cement or the like with water. More particularly, the invention relates to improvements in apparatus for continuously mixing flowable solid constituents with liquids. Still more particularly, the invention relates to improvements in apparatus of the type wherein a rotary feed screw delivers metered quantities of a solid constiutent into a mixing chamber where the solid constituent is contacted by a liquid constituent.
It is already known to utilize a rotary feed screw as a means for admitting metered quantities of cement or the like into a mixing chamber wherein the solid constituent is intimately mixed with water or the like. The feed screw comprises a solid core or shaft which carries a continuous helical thread. Alternatively, the solid constituent is fed by hollow screws which resemble a helix. A drawback of presently known apparatus is that the rotating feed screw is likely to dig a tunnel in the supply of admitted solid constituent and that the material around such tunnel forms a stagnant cylindrical body which is not advanced into the mixing chamber. This affects the accuracy of the metering action and/or causes undesirable classification of ingredients of the solid constituent. Furthermore, and since the solid constituent is constituted by or normally contains hygroscopic ingredients, the stagnant body of solid material around the feed screw is likely to form a cake which contaminates the apparatus and must be removed, at intervals, in a time-consuming operation.